71 with 3.0 and IDA40's - Setup help..

[Sam1905]

Hi, I have searched multiple posts but am still seeking answers. I have a 3.0 (79 I think) with 40IDA's. As far as I know the motor has stock cams. The carbs have:

34 Venturis
160 Main
65 Idle
175 Air Correction
F3 emulsion tubes

At higher RPM / full load she runs like a banshee, the issue is that at lower RPM's the motor is really lumpy with terrible hesitation and uneven power. It also backfires excessively especially on low rpm overrun,.

Do you see anything out of order in the above specs? If not where shall I go next?
Many thanks
Sam

[Sam1905]

I guess I should start at the beginning..

Check Valves
Timing
Set up carbs per Waynes book.....

Let me know if you see any glaring issues with the jets etc above.
Sam

[jpnovak]

This may help.
" I'd start with 36mm venturies, 155 mains, 180 A/C's and 55 idles. F3 emulsion tubes are best but they are NLA. Unless you find a good used set, you are stuck with F26's."

Weber jetting 3.0 SC

I too think you are jetted too rich. Try some 55 or 60 idle jets first since your high rpm (main jet) function seems to be fine.

Does the car respond if you turn in the idle mixture screws? It sounds like the car is loading up (way too rich) on the idle circuit.

[1QuickS]

The 34mm venturis want 145 mains. Start with 55 idle jets, you may need 60's but 55's would be my guess. F3's are good. The ability to reach max RPM is a function of the main air correction jets. Too lean (small) will cause the engine to stutter. Check out the Trouble Shooting guide lines on my site: Weber Carbs Technical

Please also see my basic tuning and setup information on the same web page, idling and part throttle response is mostly idle/progression circuit and needs to be set carefully for delightful driving performance.

Love the color/accents of your car: I've been watching it for awhile.

Cheers,

Paul Abbott

[Sam1905]

Great help - thank you.
I am on the look out for new idle jets and will start on the general tuning.
I will also post pics of the build as I get the interior in.
Thanks
Sam

[larrym]

check these if you haven't already

Weber stuff on Pelican

Tuning Webers.

Porsche 40IDA 3C Weber

Weber carb upgrade

Has anyone just bolted Webers onto a 2.7 CIS engine?

Idle off idle miss - stock 914-6

Weber jetting search - https://www.google.com/search?q=weber+jetting&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-USfficial&client=firefox-a

weber IDA jetting - https://www.google.com/search?q=weber+ida+jetting&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-USfficial&client=firefox-a

71 with 3.0 and IDA40's - Setup help..

[alfadoc]

I have zero experience tuning Webers on a Porsche, and decades of experience tuning Webers on Italian cars. I believe a lot of your problem is synchronization. With IDFs and DCNFs there is a plug that can be removed at the base of the carb, near the idle air correctors and the idle mixture screws. These passages are connected to the venturis, and to the air flow at idle. I have little brass tubes that I have threaded to fit into these plugged holes. Then I use a multi column vacuum manometer to measure flow, as is used in motorcycle shops. I disconnect all linkage, close the idle air correctors all the way, then match the highest flowing barrel to the lower flowing ones by manipulating the individual carb idle adjustments. Then you balance the barrels in the carbs with the bleeds. Works a treat on a V12 Ferrari. Probably harder to explain than to do. Hope this helps.

[haycait911]

as above, check the basics, but..............................



if it stumbles, bumps, pops and bogs, then suddenly comes on smooth at about 3K. I feel your pain. what you're describing sounds like more than just mis-jetted. and sounds exactly like my 3.0 was running.

my problem was dirty idle jets. easy to fix and costs almost nothing.

replace fuel filter first, with a good one. remove mains and float plugs and idle jet holders and let carbs drain. run pump for 30 sec to flush carbs. put mains and plugs back in.
remove idle jets from holders. have a look, I bet you see some bit of something in a couple of the jets. blow clean and look to see a clean hole. re-install in holders and screw holders into carbs.

even money your problem is solved.

your jetting is the same as my 3.0, except I have 185 a/c. and it runs kinda rich, but I like it that way. when you get the big issues sorted, get a Gunson Colortune. best tool ever to tune six individual carb throats.

see post #42 on this thread.......

Gunson Colortune / Experience Any Problems?

[mikl911]

I had the same problem under 3000 RPM I put non ethanol fuel in the tank problem solved.